Sigma USB Dock with D850

Started 10 months ago | Discussions thread
OP mholdef Senior Member • Posts: 1,986
Re: Case in point...

Bing Chow wrote:

mholdef wrote:

Hello !

Just coming back to this as I finally will have some quality time to do this now.

One question I have is why you would not use the Nikon AF Tune at each distance to give the recommended + or - values to tell you how much correction should be made for the lens at each focus distance, then enter these values with the lens.

Because the process to find the correction value with Nikon's AF Fine Tune is the exact same method of "trial and error." I don't have Auto AF Fine Tune, and even if I did, and you trust it, I don't know if the Nikon numbers translate over to Sigma 1 to 1. Recall I have a D810. So then I have to run thru my same process to verify it. So that's maybe even more work.

From what I gather from your approach and other tutorials is to do this based on trial and error looking at test shots taken with the camera, seeing if is back or front focusing - which although less "numerical" is more accurate given you are trusting your eyes looking at the screen vs. the camera.

Yes, more time consuming, but more reliable and accurate. I've said this before but it bears repeating: the time you spend firing a hundred shots gives you an appreciation of how consistent your Sigma is. You don't want 3 of 5 shots perfect, but the other two is way out in left field. You want them all clustered with the same degree of error so you can apply the needed correction. I've learned not to take just one shot and based your correction value off of that, because you could have got an outlier. The more shots the better. I've settled on 5. If you can stand doing 8 or 10, kudos to you.

A final question I have is regarding the AF fine tune values in the Nikon - should these be set at "0", as all the correction is being done with the lens through the dock ?



I do. This whole process is tedious enough. I don't want Nikon's AFFT algorithm mixing with Sigma's secret sauce, and potentially resulting in some weird behavior. Then I don't know who to blame: the lens, my testing method, or the mix of the two?

OK thanks again for all the help


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